Unlike conventional materials for the petrochemical industry, 1,4:3,6-dianhydrohexitol is a bio-based material derived from a biomass, i.e., a renewable resource containing polysaccharide as its components such as corn, wheat, potato, and the like. Particularly, a bioplastic containing a bio-based material has attracted attention as a material for reducing generation of carbon dioxide, thereby addressing the worldwide issue of global warming, since carbon dioxide generated while such a bioplastic is degraded after its use can be reused for the growth of a biomass.
1,4:3,6-Dianhydrohexitol has the following three stereoisomer types, which have different chemical properties depending on the relative configuration of the two hydroxyl groups: isomannide (Formula a below, mp: 81-85° C.), isosorbide (Formula b below, mp: 61-62° C.), and isoidide (Formula c below, mp: 64° C.).

Particularly, in case 1,4:3,6-dianhydrohexitol is used as a monomer for preparing a polycarbonate, a representative engineering plastic, the polycarbonate thus prepared can have good thermal and optical properties attributable to the molecular structural characteristics of 1,4:3,6-dianhydrohexitol, i.e., chirality and rigid saturated heterocyclic structure, together with the advantages of a bioplastic. For this reason, 1,4:3,6-dianhydrohexitol has been widely used as a representative raw material for developing bioplastics.
Meanwhile, 1,4-dimethyl-cyclohexane dicarboxylate (hereinafter abbreviated as “DMCD”) or 1,4-cyclohexanedicarboxylic acid (hereinafter abbreviated as “CHDA”), a hydrolysis product of DMCD, has a cyclohexane ring structure in its molecule center. Thus, if it is incorporated into a polymer chain, it improves not only the weatherability and UV stability of the polymer, but also such properties of the polymer as gloss retention, yellowing resistance, hydrolytic stability, corrosion resistance, and chemical resistance, owing to the unique combination of flexibility and hardness in the molecular structure.
Poly(1,4-cyclohexylidene 1,4-cyclohexanedicarboxylate) (hereinafter abbreviated as “PCCD”), a DMCD/cyclohexanedimethanol (hereinafter abbreviated as “CHDM”) homopolyester, is an example of commercially available polymer materials prepared from DMCD. By virtue of its superior weatherability, chemical resistance, flowability, and a low refractive index, PCCD has been used in developing a polycarbonate/PCCD alloy (brand name: Xyrex) by DuPont (USA) for the purpose of improving transparency of a polycarbonate.
A commercial process of manufacturing a polycarbonate can be divided into solution polymerization and melt polycondensation. Unlike the solution polymerization process where phosgene is used as a source for a carbonate, diphenyl carbonate (hereinafter abbreviated as “DPC”) is used in the melt polycondensation process. Thus, the raw materials used in the conventional melt polycondensation process generally comprise DPC and bisphenol A (hereinafter abbreviated as “BPA”) as a diol; and transesterification of BPA and DPC produces phenol as a by-product of the melt polycondensation.
The present inventors have developed a novel process for preparing an isosorbide-based polycarbonate ester, which is prepared from 1,4-diphenyl-cyclohexanedicarboxylate (hereinafter abbreviated as “DPCD”) derived from DMCD or CHDA.
The present invention employs DPCD as a material for forming an ester bond in polymer chains in the preparation of an isosorbide-based polycarbonate ester (or a polyester carbonate). The polycarbonate ester thus obtained is a novel bioplastic having excellent transparency and high heat resistance whose properties for certain usage and molding processability can be adjusted by varying the content of DPCD. The bio-based polycarbonate ester according to the present invention has excellent heat resistance, surface hardness, and impact strength as compared with the conventional bioplastic disclosed in US Patent Application Publication No. 2011/0003101 and U.S. Pat. No. 8,399,598.